How to choose air compressor lubricants correctly

How to choose air compressor lubricants correctly

Accurate selection of compressor oil for reasonable lubrication is an important measure to ensure the safe and stable operation of the compressor. Therefore, when selecting special lubricants for screw air compressors, not only working load, movement speed, working temperature, lubrication method, and operation must be considered. Environment, but also from the quality of screw air compressor lubricants.

　　1. The quality of air compressor lubricant base oil

　　The base oil of compressor oil generally accounts for more than 95% of the product oil. Therefore, the quality of the base oil is directly related to the quality level of the compressor oil, and the quality of the base oil is directly related to its refined depth. Deeply refined base oil has less heavy aromatics and gum content, low carbon residue, good antioxidant sensitivity, low carbon deposition tendency in the compressor system, and good oil-water separation. Base oil has a great influence on the performance of rotary compressor oil, so screw air compressor oil generally uses high-quality hydrogenated mineral oil or synthetic oil as the base oil.

　　2. Oxidation stability of screw air compressor lubricant

In the recycling process, the oil is constantly in contact with the high temperature and high pressure oxygen in the compressed air, and it is easily oxidized and deteriorated to produce various acids, gums, asphaltenes and other substances, which makes the oil color darker, acid value increased, and viscosity. Increase and appearance of deposits, thereby reducing the amount of oil injected, increasing the temperature of the oil and the machine, and causing excessive wear. Therefore, screw air compressor oil must have excellent oxidation stability to ensure long-term and safe use of the oil.

　　 3. Carbon deposition tendency of screw air compressor lubricating oil

　　The anti-coking tendency of compressor oil is essential to the reliable operation of compressor oil. The main substances that easily form carbon residue in oil are asphaltenes, gums and polycyclic aromatic hydrocarbons. Most of the above substances can be removed from the lubricating oil after deep refining. Generally, low-viscosity and highly refined lubricating oil has a low carbon residue value and is not easy to deposit carbon during use. The carbon deposition tendency performance of oil products is a comprehensive performance of various indicators, and there are many influencing factors. Among them, ashless additives should be used as much as possible.

　　4. Oil-water separability of lubricating oil for screw air compressor

　　 The compressor constantly meets the condensed water in the air and is stirred vigorously during operation, which is prone to emulsification, resulting in unclear oil and gas separation and increased oil consumption. As the oil is emulsified, the oil film is destroyed, causing wear. The emulsified oil will promote the dispersion of dust, grit and sludge, affect the function of the valve, increase friction, wear and oxidation. Therefore, high-quality compressor oil has good demulsification performance and oil-water separation performance.

　　5. Defoaming properties of screw air compressor lubricants

　　 In the process of recycling screw compressor oil, the circulation speed is fast, the oil is in a state of vigorous stirring, and it is easy to produce foam. When the compressor oil is started or depressurized, the oil in the oil pool is also easy to foam. A large amount of oil foam is poured into the oil and gas separator, which increases the resistance and fuel consumption, which will cause serious overload, overtemperature and other abnormal phenomena. Therefore, a good rotary compressor oil must have excellent defoaming performance to ensure that the oil has a low foaming tendency (that is, foaming) and good foam stability (that is, defoaming).

　　6. ​​Anti-rust and corrosion resistance of lubricating oil for screw air compressor

　　The compressor oil cooling and other parts are made of copper or copper metal, which is easy to be corroded, which will cause the oil to undergo early oxidation and deterioration, resulting in sludge. This requires that the oil should have good corrosion resistance. The moisture in the air is easy to cool in the intermittently operated compressor, which is not good for lubrication and can cause rust. Therefore, the compressor oil is required to have a good anti-rust effect.

　　7. Base oil fraction of screw air compressor lubricating oil

　　The composition of base oil is a key factor in judging the quality of air compressor oil. After the compressor oil, which is blended from the light and heavy two species, is injected into the compressor cylinder, its light component leaves the working part early due to its strong volatility, which affects the lubrication effect, while the heavy component has poor volatility, after completing the work task It still stays at the working part, and it will easily form carbon deposits under the action of heat and oxygen over time, which will affect the performance of the air compressor. Therefore, the lubricating oil should use narrow-fraction component oils, and should not use multiple-fraction mixed component oils.

　　 8. Viscosity of lubricating oil for screw air compressor

　　 Under the condition of dynamic lubrication, the thickness of the oil film increases with the increase of the viscosity of the base oil, but the friction force also increases with the increase of the viscosity of the base oil. Lubricating oil with too low viscosity is not easy to form a strong enough oil film, which will accelerate the abrasion of the air compressor, which will reduce the service life of the moving parts of the air compression. On the contrary, air compressor lubricating oil with too high viscosity will increase the internal friction and increase the power loss of the compressor, resulting in an increase in the oil consumption (energy consumption) of the air compressor. Deposits are formed in channels, etc. Therefore, the choice of air compressor oil with suitable viscosity is also a problem to be considered carefully. Scientific verification has shown that: using the same test conditions on the same type of compressor, using a lower viscosity oil than using a high viscosity oil z* can reduce the power loss of the compressor by about 10%, and there is no wear on the components. Significant differences. Therefore, under the premise of ensuring lubrication, choosing oils of suitable viscosity grades has a very important impact on the energy saving of the air compressor and the reliable operation of the air compressor.

　　 9. Flash point of screw air compressor lubricant 　　 Flash point refers to the temperature at which the vapor pressure formed by heating the oil under atmospheric pressure reaches the lower limit concentration ignited with an open flame. Air compressor oil with a too high flash point has a heavy oil fraction and a high viscosity, and the content of impurities such as asphalt is high, and it is easy to form coke during use. If only the high flash point of compressor oil is pursued, it will become an unsafe factor for air compressors. Therefore, the flash point of compressor oil should be moderate, and generally should be controlled above 200 ℃.

　　10. Anti-corrosion and anti-rust properties of screw air compressor lubricants

　　 Compressor oil cooling and other parts are made of copper or copper metal, which is easy to be corroded, which will cause early oxidation and deterioration of the oil and generate sludge. This requires that the oil should have good corrosion resistance. The moisture in the air is easy to cool in the compressor cylinder of intermittent operation, which is not good for lubrication and can cause wear and rust. The compressor oil is required to have a good anti-rust effect.

　　11. Consider the working load of the screw air compressor

　　 The working load is the static load and the dynamic load that the bearing (or friction pair) directly bears. It should be fully considered when selecting lubricants. Under liquid lubrication conditions, the greater the viscosity of the lubricating oil, the greater its carrying capacity; when in boundary lubrication conditions, the viscosity has little effect on improving lubrication, and its oiliness and extreme pressure resistance are indispensable. At this time, anti-extreme Lubricants with good pressure performance; for impact loads, reciprocating motion, or occasions where oil film formation is difficult, grease or solid lubricant should be used. Centrifugal compressor bearings are generally radial bearings.

　　 12. Consider the moving speed of the screw air compressor

Relative motion speed is an important parameter for the structural design of the bearing (or friction pair), and it is also a consideration for the selection of lubricants. Generally, bearings with low relative motion speeds are suitable for use with higher viscosity lubricants to facilitate the formation and maintenance of the oil film; Type compressors generally have a higher speed, some up to 10000r/min, so lubricating oil with lower viscosity should be used.

　　 13. Consider the operating temperature of the screw air compressor

The working temperature refers to the ambient temperature in which the bearing is working and the temperature that affects it. If the ambient temperature is low, lubricating oil with low viscosity and low freezing point should be selected; when the ambient temperature is high, then The lubricating oil with high viscosity and high flash point should be selected; when the temperature of the working environment where the bearing is changed is large, the lubricating oil with good viscosity-temperature performance and high viscosity index should also be selected. In short, when selecting lubricating oil, it is necessary to make it reasonable and reliable according to the temperature of the bearing working environment.

　　14. Consider the screw air compressor lubrication method

For gap-type lubrication or lubricating oil that is easy to lose, lubricating oil with good adhesion and high viscosity should be selected; centrifugal compressors generally use continuous and forced lubrication, so the relative viscosity should be small, good oxidation stability, and anti-oxidation. Lubricants with good rust, anti-foam and lubricating properties.

　　 15. Consider the operating environment of the screw air compressor

　　 If the compression medium of the compressor has special requirements for lubricating oil, the corresponding air compressor lubricating oil with resistance to the medium should be selected, such as ammonia-resistant lubricating oil for ammonia compressors. In addition, when selecting oil, refer to the lubricants recommended by the equipment manufacturer. In summary, when selecting lubricants, one is to consider the working and environmental conditions of the equipment to meet the needs of equipment operation; the other is to reduce the variety of lubricants as much as possible to facilitate the management of lubricants.